Laminating adhesives

ABSTRACT

Adhesives for laminating saran film or saran coated surfaces to polypropylene or polyethylene films or surfaces are disclosed. The adhesives comprise solutions of a mixture of a terpene urethane resin with certain thermoplastic polyether polyurethanes.

United States Patent [191 Zamer 1 June 3, 1975 LAMINATING ADHESIVES [75]Inventor:

['i J] Assignee: Inmont Corporation, New York,

[22] Filed: v Sept.l1, 1973 [2]] Appl, No.: 396,237

Joseph Zamer, Paramus, NJ.

[56] References Cited UNITED STATES PATENTS 3,442,843 5/1969 Keberle eta1. 260/292 TN 3,463,753 8/1969 Conzenbach et a]. 161/190 3,479,310 11/1969 Dieterich et a1 260/292 TN 3,656,998 4/1972 Ottmann et a1 161/1903,718,712 2/1973 Tushaus 260/775 AN Primary ExaminerGeorge F. LesmesAssistant ExaminerR. J. Roche [5 7 ABSTRACT Adhesives for laminatingsaran film or saran coated surfaces to polypropylene or polyethylenefilms or surfaces are disclosed. The adhesives comprise solutions of amixture of a terpene urethane resin with certain thermoplastic polyetherpolyurethanes.

6 Claims, No Drawings LAMINATHNG ADHESIVES This invention relates toimproved adhesives and laminates. More particularly the inventionrelates to improved adhesives that are especially suited for mak' inglaminates of saran films or saran coated films to treated polypropylenefilms. The adhesives are also suitable for laminating treatedpolypropylene surfaces to each other; also for laminating saran tosaran, saran to treated polyethylene or to other saran films orsurfaces, and to treated polyethylene to treated polyethylene. Thisinvention also relates to methods of preparing the said laminates.

The packaging industry employs enormous quantities of film, foil andanalogous sheet-like structures for protecting foods from loss ofmoisture, from the oxidative effect of air or oxygen, from thedeleterious effects of light, and for other reasons. Some of the mostuseful of these packaging films are laminates. Among the most usefullaminates are those in which saran, or a saran coated substrate islaminated to a film or sheet of treated polyethylene or treatedpolypropylene, or laminates wherein treated polyethylene or treatedpolypropylene is laminated to another treated polyethylene orpolypropylene surface. Saran is a generic name for a copolymercontaining between about 25 and 95 weight percent polymerized vinylidenechloride with the remainder being any other monoethyleneicallyunsaturated monomeric material which is copolymerizable with vinylidenechloride. Treated polyethylene or polypropylene means polyethylene orpolypropylene, foil, film, etc., which has been treated to provide asurface thereon which has better adhesion for inks, coatings andadhesives. Corona discharge treatment of the polyethylene orpolypropylene surface is the method most frequently used; however othermethods such as flame treatment and contacting the surface with chromicacid solution are reported in the prior art.

The prior art teaches the use of reactive urethane adhesives forlaminating saran to saran, for laminating treated polyethylene totreated polyethylene and for laminating saran to treated polyethyleneand polypropylene. Such prior art methods have the disadvantage that theadhesive comprises two components which have to be mixed immediatelyprior to application. Being reactive, the adhesive has a relativelyshort pot life, i.e., the setting of the reactive adhesive becomes soadvanced the viscosity build-up is so great that it becomes difficult toapply the adhesive to the substrate. A further disadvantage is thatafter application of the adhesive several hours are required for theultimate bond to be formed by the curing or setting of the adhesive.

In accordance with the present invention the above enumerateddisadvantages are overcome by employing an adhesive comprised of amixture of thermoplastic water soluble polyurethane and a waterinsoluble thermoplastic terpene urethane as the adhesive for laminatingsaran surfaces to treated polyethylene or polypropylene surfaces, orsaran surfaces to saran surfaces, or treated polyethylene orpolypropylene surfaces to treated polyethylene and polypropylenesurfaces.

The novel adhesives of the present invention have unique and unexpectedproperties. For instance, while it was previously known that certainwater soluble thermoplastic polyurethanes, such as those used in thepresent invention, are excellent adhesives for laminating treatedpolyethylene to itself or to saran surfaces, such water solublepolyurethanes do not provide good adhesion of treated polypropylene toitself or to saran surfaces. It was, therefore, surprising andunexpected that blends of these water soluble polyurethanes with minoramounts of a water insoluble terpene polyurethane would provide anadhesive that would bond treated polypropylene to itself or to saran.The results are even more surprising in view of the fact that theterpene polyurethane alone is not a good adhesive for laminating treatedpolypropylene to itself or to saran surfaces. The novel adhesivecomposition is, therefore, an important feature of the invention.

Another important embodiment of the invention is a heat-scalable,essentially moisture-proof and greaseproof laminated film structurecomprised of a layer or film of treated polyethylene or polypropylenelaminated to a preformed substrate layer or sheet of saran or sarancoated substrate such as saran coated cellophane, saran coatedpolyester, saran coated nylon, or saran coated polypropylenepwherein thelaminating adhesive is a blend of (a) an essentially thermoplasticpolyurethane prepared from polyurethane forming reactants, usingconventional catalysts wherein at least one of the reactants contains atertiary nitrogen atom which imparts sufficient basic ity to the polymerto enable it to form water soluble salts with carboxylic acids and. (b)a minor amount of a terpene polyurethane which is insoluble in water.

The thermoplastic water soluble polyurethane is a polyether polyurethaneand is prepared from a polyalkylene glycol, a diisocyanate, and anN-phenyl or N- alkyl-dialkanolamine. Preferably a difunctional chainextender reactant will be included as a reactant, such as a glycol or analkylene diamines. An alkylene diamine chain extender is preferred.

Although polypropylene glycol having a molecular weight of 400 to 4,000is preferred as the polyalkylene glycol component because of economicsand better properties, other polyalkylene glycols, especiallypolyethylene, can be used in preparing polyurethanes that are operablein the invention.

The diisocyanates useful in preparing the thermoplastic polyetherurethanes used in the present invention are those conventionally used inpreparing polyurethane resins and include, for instance, methylenediphenyl isocyanate, toluene diisocyanate, hexamethylene diisocyanate,isophorone diisocyanate and hydrogenated methylene diphenyl isocyanate.The aliphatic diisocyanates, such as hexamethylene diisocyanate,isophorone diisocyanate, and the hydrogenated aromatic diisocyanates,such as hydrogenated methylene diphenyl isocyanate, are preferred wherelight stability is important.

The N-alkyl dialkanol amine reactants useful in preparing thethermoplastic polyurethane comprise such reactants in which the alkylgroup is a lower alkyl group, i.e., an alkyl group containing one to sixcarbon atoms and the alkanol groups contain one to four carbons. Thealkyl group may be a straight chain alkyl group, a branched chain alkylgroup or a cyclo-aliphitic hydrocarbon group. A preferred N-alkyldialkanol amine is N-methyl diethanol amine which is preferred foreconomic reasons as well as for overall optimization of properties.

The preferred chain extender, when used, is an aliphatic diamine such asethylene diamine, propylene diamine, butylene diamine and hexamethylenediamine or an alkanol amine such as ethanol amine. Ethylene diamine isespecially preferred.

Polyether polyurethanes useful in the invention are prepared by reactingthe desired N-phenyl or N-alkyl dialkanol amine and polyether diol withan excess of the desired diisocyanate, up to an NCO to OH ratio of :1excess of diisocyanate on a molar basis being used. The reactionpreferably is carried out in a volatile inert water miscible organicsolvent such as water miscible ketones, ethers and esters. Methyl ethylketone is especially preferred. The reaction is continued, by heating tothe reflux tempe; at'rre of the solvent if desired, until reaction iscomplete as indicated by a substantially constant isocyanate (NCO)assay. At this point the polyurethane may be capped, or terminated, byreacting the remaining isocyanate groups with a monofunctional loweralcohol, such as isopropanol, but in most cases the polyurethane polymerwhich still contains isocyanate groups is preferably chain extended withan alkylene diamine to obtain a preferred molecular size and theresulting chain extended polyurethane which still contains someunreacted isocyanate groups is capped with excess isocyanate reactantsuch as water miscible alcohol, hydroxycarboxylic acid, or water.

For polyether polyurethanes to be useful in the present invention, it isnecessary that they contain 2.0 to 8.0% by weight, preferably 3 to 5% byweight, of nitrogen derived from isocyanate groups. In general thehigher percentages of nitrogen produce harder polymers while the lowerpercentages of nitrogen produce softer polymers. Polymers containing 3to 5% by weight of isocyanate derived nitrogen and 0.75 to 1.5% byweight of tertiary amine derived nitrogen are preferred because theyprovide the most desirable combination of adhesive bond strength.Generally the reaction of the prepolymer containing isocyanate groupswith the diamine chain extender is carried out at a temperature range onthe order of 25 to 70C. The reaction is carried out stepwise to avoidvariations in molecular weight from batch to batch. Ordinarily thedesired degree of chain extension will be achieved when an isocyanateassay of about .005 to .20 milliequivalents of NCO per gram of solutionat 50% by weight solids is obtained. Isocyanate assay is determined on asmall sample of the reaction mixture by reacting the isocyanate withexcess dibutyl amine, back titrating the excess amine with acid and thencalculating the milliequivalents of NCO after correcting for the amountof tertiary amine groups in the polymer.

The amount of N-phenyl dialk'anol amine or N-lower alkyl dialkanol amineused in the polymer can be sufficient to produce a polymer containing onthe order of 0.5 to 2.5% by weight, of tertiary nitrogen, or enough tomake the polymer soluble in aqueous acidic solutions. Ordinarily saltsof the polymer become soluble in water when the polymer contains atleast about 0.5% by weight of tertiary nitrogen. The upper limit oftertiary nitrogen content is not critical for water solubility as thesalt but for optimum properties for use in the present invention it ispreferred that the upper limit of tertiary nitrogen content should notexceed about 2.5% by weight of the polymer.

When the polymer size that is desired has been obtained, preferably bychain extension as described herein above, and a polymer having anisocyanate assay on the order of .005 to .20, preferably .07 to .1,milliequivalents of NCO preferably .07 to .l milliequivalents of NCO isobtained the polymer is capped, or terminated by reacting the remainingisocyanate groups with an excess of isocyanate reactant, preferably awater miscible alcohol, e.g., isopropanol, ethanol, water, lactic acid,etc. Any large excess of the water miscible alcohol solvent that isadded as the isocyanate reactant to terminate or cap the polymer mayalso serve as a solvent for the polymer.

The prereacted, capped, thermoplastic polyether urethane is converted toa water soluble salt by reacting with the appropriate amount of an acid.Although acids in general, both organic acids and mineral acids, areeffective to solubilize the polymer, the preferred acids to use are thesubstantially non-toxic organic carboxylic acids, especially acids thathave been approved by the Food and Drug Administration for use in foodsand food packaging. Lactic acid is such an acid and is very suitable foruse in the present invention. Although the upper limit of the amount ofacid to use is not particularly critical, it has been found that thelower limit is critical and that at least about of the theoreticalamount required to neutralize the polymer must be used to solubilize it.Increasing the amount of acid above the minimum required to solubilizethe polymer tends to increase the viscosity of the solution and thusprovides a convenient means of regulating the viscosity for applicationpurposes.

An adhesive composition in accordance with the invention is prepared bymixing the solution of the salt of the polyurethane as described abovewith a solution of the desired amount of water-insoluble terpenepolyurethane resin, i.e., 0.2 to 1 part by weight of terpenepolyurethane resin, preferably 05 part, for each part by weight of watersoluble polyurethane. Preferably the terpene polyurethane resin will bedissolved in a water miscible, volatile solvent such as a lower alcoholor ester. For convenience in handling, and economy in shipping, theadhesive composition preferably is prepared as a 30% solids solution, orhigher. For application it may be diluted to the concentration andviscosity which is desired for the particular application.

The terpene-urethane resins, or terpene polyurethane resins, as usedherein refers to resins made by reaction of terpene alcohols withpolyisocyanates, especially diisocyanates. Such resins are availablecommercially and are described in the prior art. In the presentinvention we especially prefer a product that is described by thesupplier as a terpene-urethane resin, soluble in aromatic and aliphatichydrocarbons, esters and chlorinated hydrocarbons, having limitedsolubility in alcohols and ketones, having a color of l (Gardner Scale),a specific gravity of 0.95 1.05 and a melting point of C i 5C.

The following Examples in which the parts are by weight are given tofurther illustrate the invention:

EXAMPLE 1 A reaction mixture consisting of:

Parts Polypropylene glycol, M.W. of 1007,

Hydroxyl No. 108 483 N-Methyl diethanolamine 64.4 Toluene diisocyanatel95 Dibutyltin dilaurate (catalyst) 0.35 Methyl ethyl ketone 743.0

was heated at reflux until an NCO assay of between 0.13 and 0.16 wasobtained. At this point the temperature was reduced to 6065C. and acalculated amount of ethylene diamine was added to lower the NCO assayvalue to 0.07 milliequivalents per gram. The calculation of the amountof ethylene diamine was made as follows:

Grams ethylene diamine required (milliequivalents of NCO per gram 0.07)X batch weight in grams Mol. Weight of ethylene diamine/2,000.

Reaction between the ethylene diamine and isocyanate prepolymer is rapidand is assumed to be complete within a few minutes after which time1,060 parts of methyl ethyl ketone and 82.5 parts of lactic acid (88%technical grade) was added and the reaction mixture cooled to roomtemperature. The resulting chain extended polyether polyurethane resinsolution contains 30% solids by weight. An adhesive is prepared bydissolving a terpene-urethane in a diluted solution of the above chainextended polyether polyurethane as follows:

Parts 30% Solution of polyether polyurethane 500 Methyl ethyl ketone I75lso-terp 95 resin 75 and then diluting the solution with 750 parts ofmethyl ethyl ketone. The resulting adhesive contains by weight solidsand is of suitable viscosity for application by gravure roll. It wasapplied to saran film or to saran coated cellophane, or treatedpolyethylene, or treated polypropylene surface at a rate ofapproximately 0.5 pounds/ream (3,000 square feet); the solvent is evaporated, and the adhesive coated surface is then adhered to the desiredsurface such as treated polyethylene or polypropylene, or saran, byconventional laminating techniques to give packaging laminate filmshaving ultimate bond strengths immediately at the end of the laminator.Immediate ultimate bond strengths on the order of 350 to 600 grams areeasily obtainable even when laminating a saran surface to apolypropylene surface.

Bond strengths as used in the present application are measured on anAmthor Tensile Tester, Type 272 (available from Amthor TestingInstrument Co., 45-53 Van Sinderen Avenue, Brooklyn, NY.) and is theforce, in grams, required to separate the laminate using a 1 inch widestrip of laminate and ajaw separation rate of 12 inches per minute.Initial bond strength of at least 350 grams is required for asatisfactory laminate. If lower bond strengths are obtained, itindicates that all solvents were not removed from the adhesive filmprior to lamination. In such cases, it is only necessary to adjust thedrying ovens to ensure complete removal of solvents. Drying temperatureson the order of 190 to 220 are preferred.

Methyl ethyl ketone was heated at reflux until a constant NCO assay of0.141 was obtained. A calculated amount of ethylene diamine, sufficientto lower the NCO assay to 0.07 milliequivalents/gram of 50% solution,and then 105 parts of an 88% lactic acid solution in water was added andthe reaction mixture was stirred for 15 minutes. Then 1,414 parts ofisopropanol was added to form a clear solution of resin, 30% solids byweight, having a viscosity of 250-700 centipoises at 25C. The polymercontains 3.95% by weight of N derived from isocyanate and 1% by weightof tertiary N. An adhesive composition is prepared by dissolving aterpene-urethane in a diluted solution of the chain extended polyetherpolyurethane as follows:

Parts 30% Solution of polyether polyurethane 500 Methyl ethyl ketone Ilso-terp resin 75 and then diluting the solution with 750 parts of ablend of equal parts by weight of methyl ethyl ketone and isopropanol.The resulting composition is used as an adhesive in a manner similar toExample I to form laminates having bond strengths of more than 350grams.

What is claimed is:

l. A laminate of the group consisting of saran adhesively bonded tosaran, saran adhered to treated polyethylene or treated polypropylene,and treated polyethylene adhered to treated polyethylene wherein theadhesive is a mixture ofa minor amount of a terpene urethane resin whichis the reaction product of a terpene alcohol with a polyisocyanate, anda major amount of a water soluble salt of a substantially linearthermoplastic polyurethane containing 0.5 to 2.5% by weight of nitrogenderived from tertiary amine groups and from 2 to 8% of nitrogen derivedfrom isocyanate groups, said polyurethane being prepared by (a) reactingan excess of an isocyanate with a mixture of diols consisting ofpolyether diols having a molecular weight of from 425 to 4,000 andtertiary amine diols selected from the group consisting of N-phenyldialkanol amine and N- lower alkyl dialkanol amines to obtain a reactionproduct having free isocyanate groups greater than 0.1 milliequivalentsof NCO per gram of solution at 50% solids, (b) chain extending thereaction product with a chain extender selected from the groupconsisting of alkanol amines and alkylene diamines to obtain a chainextended polyurethane polymer containing from 0.07 to 0.1milliequivalents of NCO per gram of 50% solution, (c) reacting the freeisocyanate groups with a material selected from the group consisting ofwater miscible alcohols, water miscible acids and water, an amount of awater miscible acid being added sufficient to form the acid salts of thetertiary amine groups present on the polyurethane.

2. A laminate as in claim 1 wherein the polyether diol is polypropyleneglycol, the N-Iower alkyl dialkanol amine is N-methyl diethanol amineand the acid is a non-toxic organic carboxylic acid.

3. A laminate as in claim 1 wherein the polyurethane is reacted with anexcess of a water soluble alcohol and the acid is a non-toxic organiccarboxylic acid.

4. A laminate as in claim 3 wherein the isocyanate reactant is aisopropanol.

5. A laminate as in claim 1 wherein the percentage of isocyanate derivednitrogen of the polyether polyurethane is 3 to 5% by weight and thetertiary nitrogen amine is N-methyl diethanol amine, the chain extenderis 0.75 to 1.5% by weight. is ethylene diamine, and the capping agent isispr0pa- 6. A laminate as in claim wherein the polyether diol no]. ispolypropylene glycol, the N-lower alkyl dialkanol

1. A LAMINATE OF THE GROUP CONSISTING OF SARAN ADHESIVELY BONDED TOSARAN, SARAN ADHERED TO TREATED POLYETHYLENE OR TREATED POLYPROPYLENE,AND TREATED POLYETHYLENE ADHERED TO TREATED POLYETHYLENE WHEREIN THEADHESIVE IS A MIXTURE OF A MINOR AMOUNT OF A TERPENE URETHANE RESINWHICH IS THE REACTION PRODUCT OF A TERPENE ALCOHOL WITH APOLYISOCYANATE, AND A MAJOR AMOUNT OF A WATER SOLUBLE SALT OF ASUBSTANTIALLY LINEAR THERMOPLASTIC POLYURETHANE CONTAINING 0.5 TO 2.5%BY WEIGHT OF NITROGEN DERIVED FROM TERITARY AMINE GROUPS, AND FROM 2 TO8% OF NITROGEN DERIVED FROM ISOCYANATE GROUPS, SAID POLYURETHANE BEINGPREPARED BY (A) REACTING AN EXCESS OF AN ISOCYANATE WITH A MIXTURE OFDIOLS CONSISTING OF POLYETHER DIOLS HAVING A MOLECULAR WEIGHT OF FROM425 TO 4.000 AND TERTIARY AMINE DIOLS SELECTED FORM THE GROUP CONSISTINGOF N-PHENYL DIALKANOL AMINE AND N-LOWER ALKYL DIALKANOL AMINES TO OBTAINA REACTION PRODUCT HAVING FREE ISOCYANATED GROUPS GREATER THAN 0.1MILLIEQUIVALENTS OF NCO PER GRAM OF SOLUTION AT 50% SOLIDS, (B) CHAINEXTENDING THE REACTION PRODUCT WITH A CHAIN EXTENDER SELECTED FROM THEGROUP CONSISTING OF ALKANOL AMINES AND ALKYLENE DIAMINES TO OBTAIIN ACHAIN EXTENDED POLYURETHANE POLYMER CONTAINING FROM 0.07 TO 0.1MILLIEQUIVALENTS OF NCO PER GRAM OF 50% SOLUTION, (C) REACTING THE FREEISOCYANATE GROUPS WITH A MATERIAL SELECTED FROM THE GROUP CONSISTING OFWATER MMISCIBLE ALCOHOLS, WATER MISCIBLE ACIDS AND WATER, AN AMOUNT OF AWATER MISCIBLE ACID BEING ADDED SUFFICIENT TO FORM THE ACIDS SALTS OFTHE TETIARY AMINE GROUPS PRESENT ON THE POLYURETHANE.
 1. A laminate ofthe group consisting of saran adhesively bonded to saran, saran adheredto treated polyethylene or treated polypropylene, and treatedpolyethylene adhered to treated polyethylene wherein the adhesive is amixture of a minor amount of a terpene urethane resin which is thereaction product of a terpene alcohol with a polyisocyanate, and a majoramount of a water soluble salt of a substantially linear thermoplasticpolyurethane containing 0.5 to 2.5% by weight of nitrogen derived fromtertiary amine groups and from 2 to 8% of nitrogen derived fromisocyanate groups, said polyurethane being prepared by (a) reacting anexcess of an isocyanate with a mixture of diols consisting of polyetherdiols having a molecular weight of from 425 to 4,000 and tertiary aminediols selected from the group consisting of N-phenyl dialkanol amine andN-lower alkyl dialkanol amines to obtain a reaction product having freeisocyanate groups greater than 0.1 milliequivalents of NCO per gram ofsolution at 50% solids, (b) chain extending the reaction product with achain extender selected from the group consisting of alkanol amines andalkylene diamines to obtain a chain extended polyurethane polymercontaining from 0.07 to 0.1 milliequivalents of NCO per gram of 50%solution, (c) reacting the free isocyanate groups with a materialselected from the group consisting of water miscible alcohols, watermiscible acids and water, an amount of a water miscible acid being addedsufficient to form the acid salts of the tertiary amine groups presenton the polyurethane.
 2. A laminate as in claim 1 wherein the polyetherdiol is polypropylene glycol, the N-lower alkyl dialkanol amine isN-methyl diethanol amine and the acid is a non-toxic organic carboxylicacid.
 3. A laminate as in claim 1 wherein the polyurethane is reactedwith an excess of a water soluble alcohol and the acid is a non-toxicorganic carboxylic acid.
 4. A laminate as in claim 3 wherein theisocyanate reactant is a isopropanol.
 5. A laminate as in claim 1wherein the percentage of isocyanate derived nitrogen of the polyetherpolyurethane is 3 to 5% by weight and the tertiary nitrogen is 0.75 to1.5% by weight.